Answer:
24
Step-by-step explanation:
Let's say that R, N, and M are the ages of Ric, Nancy, and Michael in 1980.
We can write three equations:
R = 2N
N = 2M
(R + 12) + (N + 12) + (M + 12) = 78
Simplify the third equation:
R + N + M + 36 = 78
R + N + M = 42
Substitute the first equation:
2N + N + M = 42
3N + M = 42
Substitute the second equation:
3(2M) + M = 42
6M + M = 42
7M = 42
M = 6
Therefore:
N = 12
R = 24
